These are two terms that are similar but distinct in their meaning and, unfortunately, often used interchangeably by the press when writing about health care and clinical practices. The primary purpose of this post is to sensitize readers that news stories can be misleading when writers are careless in choosing between them.

In clinical practice, to "detect" a problem is to objectively observe symptoms caused by the problem or to hear a subjective but credible complaint from the patient about a symptom that is not visible (i.e. back pain). To "diagnose" a problem is to ascertain the specific medical condition that is causing the problem.

Here is an example from the field we follow. A physician would "detect" memory loss by objectively establishing that a patient's recall ability is not in the normal range for the patient's age and educational peer group. The physician need not know the cause of the problem to detect it.

Once detected, the memory loss would then be "diagnosed" as (for example) a thyroid disorder, or as Alzheimer's disease, or as any number of other memory impairing medical conditions. The diagnosis informs the forthcoming decisions about treatment.

In general, much of the news about neuro-psychological tests being developed is news about improving our ability to detect problems. Much of the news about bio-markers is news about improving our ability to diagnose problems. In the realm where I see the most common misuse of these terms, much of the news about imaging techniques crosses between the two.